I don't have an answer but it reminds me of the little guides on a sewing machine that keep your thread where it should go. It's pretty cool. I didn't know there were so many thimble types available.
I think so too! I know, did you look up thimbles on eBay? I was amazed, I had no clue either and some sell for quite a bit of money.
I googled them and looked at some different websites. There are some really cool thimbles out there. I saw one that you wear when you are knitting that guides two different colors of yarn. I hope you find what it is. Let us know :)
If you go to google images and look up vintage thimble threader there are several pictures similar to yours. it looks like they are supposed to have a wire loop on the end of that hinged piece to allow for threading. Some of the listings also state that they are thread cutters. Hope this helps! :-)